A. Field of the Invention
The present invention relates generally to apparatus and methods for logging and servicing bore holes and more particularly to an apparatus and method for logging and serving both vertical and highly deviated bore holes with logging or servicing tools run into the bore hole on the end of a string of pipe which allows the logging or servicing tools to be manipulated with respect to the string of pipe.
B. Description of the Prior Art
An important aspect of the field of drilling, completing, and servicing oil and gas wells involves the use of well logging and well servicing instruments. These instruments are commonly called tools and the operation of these tools is referred to as logging or servicing. Logging involves placing tools in the bore hole drilled in the earth for the purpose of locating or identifying subterranean formations and extracting oil, gas, water, or other minerals. For example, some of these tools or combinations of tools are used to evaluate general lithological structure, including formation resistivity, porosity, matrix, or fluid or gas content. Measurements include acoustics, resistivity, temperature, pressure, natural radiation, induced radiation, and many others. Other tools are used for core sampling, cementing, perforating casing or tubing, and other tests.
In some instances, it is necessary that the tool be positioned in a certain relationship to the bore hole wall. For example, compensated density tools and compensated neutron tools have a pad that is extendd outwardly from the tool into contact with the bore hole wall. The pad must be in such contact in order for the tool to preform properly. Other tools, such as mandrel neutron tools, require close proximity to the bore hole wall. Core sample tools require an optimum spacing from the bore hole wall in order to achieve maximum efficiency. In other instances, centralization in the bore hole is required for operation of such tools as dip meters or sonic tools.
Several systems are used to transport tools into and out of bore holes in order to perform their specialized operations. One conventional system uses a wireline as the conveyer. The wireline includes at least one conductor for providing electric communication for the tool to the surface and the tool is lowered on the wireline by gravity into a position to log the bore hole. In many cases of deviated holes with inclinations above 55 degrees, and in some cases less depending upon hole conditions, gravity does not provide sufficient force to move the tools down the hole and wireline logging is impossible.
A system that has been developed to log highly deviated tools includes positioning a string a drill pipe near the zone of interest and pumping a wireline with an assembly of small diameter tools out the bottom end of the drill pipe and allowing the tools to fall by gravity through the zone of interest. A very high angle bore hole can be traversed by this method as long as the open hole inclination in the zone of interest is low in angle and hole conditions permit the tool to fall by gravity. The bore hole is logged by extracting the cable and pulling the tool through the zone of interest. The pump down system is of limited untility because the small sized tools are typically of lesser quality as regards to accuracy and quality of measurement than are the larger suites of tools used in conventional wireline operations. Also, the pump down system is limited to certain hole profiles and relatively short logging zones. Additionally, the tools may be lost due to sticking. A further shortcoming of the pump down system lies in the fact that gravity provides the only means for orienting the tools.
Another system for logging high angle bore holes is disclosed in Escaron U.S. Pat. No. 4,349,072, in which the tools are lwored using a drill pipe as the conveyer and pumping an extension with a wet connector down the drill pipe into electrical connection with the tools. The tools are released and moved axially into the bore hole with respect to the drill pipe. The hole is logged by pulling the tool back into the drill pipe with a wireline. In Barry, et al. U.S. Pat. No. 3,957,118, measurement-while-drilling-type logging is conducted using a wet connector and cable stored within the drill pipe. The tools are secured at the lower end of the drill pipe above the bit and tool positioning is controlled and limited by the drilling operation.
Base U.S. Pat. No. 4,062,551, Tricon U.S. Pat. No. 4,200,297, and Marshall U.S. Pat. No. 4,388,969 each disclose systems that include a side-entry sub secured in the drill string to provide communication between tools and the surface by means of a wireline. The tools are pumped down the drill pipe to a predetermined location and the tools are conveyed into and out of the well bore by adding and removing drill pipe above the side-entry sub. Initially, the above systems were used in connection with steering tools in bent sub mud motor drilling. More recently, as disclosed by the Marshall U.S. Pat. No. 4,388,969, the systems have been used in logging. Wittrisch U.S. Pat. No. 4,457,370 discloses a system similar to what is disclosed in Marshall U.S. Pat. No. 4,388,969 and Barry, et al. U.S. Pat. No. 3,957,118 or Escaron U.S. Pat. No. 4,349,072, in which the tools are secured to the bottom of the drill string and a wet connector is pumped down to the tools via a side-entry sub. Again, the tools are conveyed into and out of the well bore by adding and removing sections of drill pipe above the side-entry sub. The tools are oriented within the well bore by rotating the drill string.
In practice, especially in deviated holes with depths from 3,000 to 20,000 feet or more, rotation or other manipulation of the drill string from the surface in order to orient tools at the bottom of the drill string is impractical due to the elasticity of the drill pipe and drag on the bore hole walls. Although orientation can be achieved with some difficulty, it is extremely difficult to maintain that orientation. The difficulty in maintaining the orientation is primarily due to torque build up in the drill string during the act of rotation from the surface. Normally, after logging a few hundred feet or less, the build up of torque or torque generated by moving the drill pipe through a corkscrew profile will rotate the tool out of position. Positioning the tool becomes even more difficult once the side-entry sub has been lowered into the well bore. After the side entry sub has been lowered, the wireline extends up to the surface along the outside of the drill pipe. With the wireline in the annulus, it is preferable not to rotate the drill string because such rotation can wrap the wire line about the drill string which can result in damage to the wire line or prevent its emergency extraction.
It is therefore an object of the present invention to provide an apparatus and method for logging bore holes and servicing wells that overcomes the shortcomings of the prior art. More particularly it is an object of the present invention to provide an apparatus and method for logging bore hole formations and servicing wells that is applicable from vertical through high deviations that are not accessible with standard wireline techniques. It is a further object of the present invention to provide a conveyer for positioning tools in a well bore that allow for rotation or other manipulation of the tools to selected orientations without rotating or manipulating the conveyer at the surface. It is yet a further object of the present invention to provide an improved system for performing downhole operations.